Summer RV system review

I hope I'm not misunderstanding, so your 3 months in summer is acceptable as a part time resident (6 months max).
So you are allowed to use your black water tank for septic and skip the whole fiasco of a new septic installation?

Black Water
Can you use the water from the stream for your black water tank, maybe filter it first if that's a concern.
You might try extending the time before needing to empty the black water tank if you limit it to No. 2 only.
Go No.1 in a bucket and dilute it with stream water and then use it to water the plants/trees near you.
https://www.scientificamerican.com/article/human-urine-is-an-effective-fertilizer/


Grey Water
I'd recommend using rainwater for washing and bathing.
Whenever it rains just set out plastic sheeting and drain into a container.
If you want an estimate, size the sq footage of plastic sheeting you have and use the following link.

Since you've got 12 acres, would there be any issues with watering the plants/trees with your grey water?
Water is easy to evaporate especially during the summer months.
You just need to let it spread out on something with a lot of surface area.
I'd setup a fold out table and lay a piece of sheet metal with low sides on it to contain the water.
Let that water bake off in the summer sun, disinfect water beforehand if that is a concern.
If there is any, scrape up the leftover scum and put it in the garbage.

White Water
I do not have access to drinking water where I am.
I use x4 7 gallon containers and since I use about 2 liters a day, I refill them every 2 months about 30 min. away.
For 2 people, then around a gallon a day should be enough for drinking/cooking.
With 30 gallons, then you'd only have to fill up once a month.
To make your monthly trips more convenient, you could refill drinking water containers whenever you empty your black water tank every 30 days.

If these options can work for you, you may not need to haul around so much water. It sounds like most of your water needs are available on site.

Greta Gremlin we get water by the gal from town. 1.5 gals per day for drinking and cooking. Shower and toilet water comes from the nice neighborhood residents. Legally the stream water is off limits. Im not sure if collecting rain water is allowed. Dumping grey water or black is not allowed because of stream contamination. Some residents there still have out houses and no septic and get there water from the stream But they are grandfathered in so they have power. To drill a well in mountain rocks can be tens of thousands of dollars. There is county water on my property but I have to get septic to have access to it. I think the year was 2014 in Virginia they changed all the laws its a clean water act. Im originally from sc 30 minutes from Myrtle beach. Im used to rivers and lakes abundance of water. But in the mountains water is scarce. Every 2 weeks i have to dump grey water 40 gal tank but I let it drain to the 40 gal black water tank that i changed for more capacity. Then drain both tanks at the rv campsite. I have to get receipts to show im not dumping on the ground.

The only thing then I would look into is maybe finding a way to evaporate your grey water if you want to make fewer trips to empty the tank.
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As for solar, offgrid solar can be closer to being worry-free and generator-free,
If you make your needs proportional to the available sunlight.
If used this way, your batteries are mainly there to provide a stable source of power.
The further you stray outside this, the closer you are to having a money pit and/or a high maintenance system on your hands.

If you have 400 watts of panels and it is sunny, then look to store the needed end result if you can.
For refrigeration, you might think about using a mini freezer to freeze containers of water.
Then store the ice in a heavily insulated cooler. The bigger the cooler, the more cold you can have stored.
For pumping water, maybe try storing it to power a gravity fed system if not using already.
For keeping cool, you can run a fan while the sun out.

This is also viable on cloudy/rainy days as well.
If you have 400 watts of panels and it is a cloudy/rainy day, then you might be able to use loads less than 40wh per hour without taxing the batteries.
The smaller the loads, the less you will have to concern yourself with that.
This could work for loads like a TV, laptop, smartphone, or possibly even a mini fridge.
I would check to see how much your panels output during those conditions to give a better idea of what could be used.

So instead of a solar system that charges/discharges batteries,
You could look into designing your system around overpaneling and only using it when panels are outputting.
May help with the extended cloudy/rainy streaks.
Essentially,
sunny=big loads
cloudy/rainy & morning & evening=small loads
nighttime=no loads

One important thing is making sure the charge controller can handle the output of the solar panels and can safely charge the battery.
I don't recommend getting a bunch of panels and running loads like air conditioners or dish washers or microwaves.
This video may have the story about the person whose family was killed due to an electrical error. A lot of good and sobering information.

Just from stories like that, there are so many variables and things that could go wrong, I'd recommend trying to keep it simple, safe, and manageable.